What do you mean by "storage"? Short term storage only, like batteries? This would lead to an overly large renewable installation to power the country in the winter.
The round trip efficiency of hydrogen is indeed bad, but for long term storage that's is overwhelmed by the much lower cost of hydrogen storage capacity, vs. batteries.
The round-trip efficiency isn't actually that bad once you realize that we're dealing with large installations here. For instance, heat can be used to make hydrogen, which is why you sometimes hear about nuclear power making hydrogen. Large installations can recapture heat, either as co-generation or use it to drive a gas turbine.
You can look at the assumptions under https://model.energy/ which were based on cost data in Europe (I believe there's a link to the source).
Per-kW cost of electrolysers is already 1/2 of the total per-kW cost given there in the 2030 assumptions (but that may include other equipment).
Cost of storage caverns is well known from natural gas, as little as $1/kWh of capacity. Cost of combined cycle plants to convert the hydrogen back to power is also well known, as these will be nearly identical to natural gas fired CC plants (just the details of the combustors will change.)
The round trip efficiency of hydrogen is indeed bad, but for long term storage that's is overwhelmed by the much lower cost of hydrogen storage capacity, vs. batteries.